Let's say you have a set of files.
Some are writable by you, others are read-only.
You want to give people in your group the same permissions you have - that
is, they can write writable files but can only read the read-only files.
It's easy with an underdocumented feature of
chmod
:

%
chmod g=u *

That means "for all files (
*
), set the group permissions
(
g
) to be the same as the owner permissions (
u
)."
You can also use the letter
o
for others, which is everyone
who's not the owner or in the owner's group.
Article
22.2
explains these categories.

If your
chmod
has a
-R
(recursive) option, you can make the
same change to all files and directories in your current directory and
beneath.
If you don't have
chmod -R
, use this
find
(
17.10
)
:

%
find . -exec chmod g=u {} \;

The
cpmod
(
22.16
)
program on the CD-ROM can copy all file permissions.